Research will be carried out on compounds that inhibit the deaminations of the antitumor agents, arabinosylcytosine and arabinosyladenine. Specifically, adenosine deaminase and cytidine deaminase will be purified from murine tumors and/or murine tissues for enzymatic studies at the molecular level. These enzymatic studies will be used to design and carry out survival studies in tumor bearing mice treated with drug combinations of nucleoside analogs and deaminase inhibitors. In addition, enzymatic, metabolic, and murine survival studies will be done with the 3', 5'-cyclic phosphate derivative of methylthioinosine utilizing murine tumors resistent to the nucleoside due to lack of adenosine kinase activity. BIBLIOGRAPHIC REFERENCES: LePage, G. A., Worth, L.S., and Kimball, A.P., Enhancement of the Antitumor Activity of Arabinofuranosyladenine by 2'-Deoxycoformycin, Cancer Res. in press, 1976. Epps, D., Chang, I.M., Sherwood, E., and Kimball, A.P., Feedback Inhibition by 6-Methylthioinosine-3', 5'-cyclic monophosphate in Tumor cells Resistant to the Nucleoside, Proc. Soc. Extl. Biol. Med., in press 1976.